Hydrogel Microelectromechanical System (MEMS) Resonators: Beyond Cost-Effective Sensing Platform

Mechanical resonators have been used for various applications including timing references, filters, accelerometers, and inertial sensors. Mostly, silicon-based materials have been thought to be ideal considering robustness and stability and thus used to fabricate micro and nanoscale mechanical resonators. When enhanced sensitivity becomes more important than long-term stability, materials repertoires other than silicon might be better suited. Herein, a novel manufacturing approach is proposed, which rapidly fabricates microelectromechanical system resonators with hydrogel by single UV exposure via dynamic mask and dry-state "plugging out" sacrificial process where hydrogel structures are defined by spatially modulated UV light. For practical demonstrations, rectangular cantilevers and closed circular membranes are employed for humidity and pressure sensing applications, respectively. The cost-effective fabrication route suggested herein not only enables rapid prototyping of suspended hydrogel structures outside a cleanroom, but also offers spatially tunable elastic modulus. Most remarkably, sensitivity enhancement resulting from high swelling rate and/or low elastic modulus exceeds stability deterioration, one of the major concerns for polymeric materials. Such exclusive beneficial features, yet demonstrated with any microfabrication materials and methods or their combinations, open a new avenue for photocurable polymeric materials to be used for specific applications as well as fundamental investigations.